CNTs are cylindrical molecules of carbon atoms, wherein the carbon atoms are arranged in a hexagonal lattice. High-quality CNTs are several times stronger than steel piano wire, despite the fact that piano wire is roughly four times as dense. CNTs are also at least five times more thermally conductive than copper, and have very high electrical conductivity and current-carrying capacity.
As a result, CNTs belong to a class of nanomaterials that have remarkable physical and mechanical properties. Their superlative mechanical properties make them a desirable filler material for composite reinforcement. Attempts have been made to disperse CNTs into a polymer matrix as a filler, thereby reinforcing the polymer. To apply the superior properties of CNTs to composites, it is sometimes desirable to disperse CNTs in matrix materials uniformly, and increase the coherence at the interfaces of CNTs and matrix materials.
When using CNTs to reinforce poly(methyl methacrylate) (PMMA), several dispersion methods such as melt blending (Z. Jin, et al. CHEMICAL PHYSICS LETTERS, 337, 43-47 (2001)), in-situ polymerization (Z. Jia, et al. MATERIALS SCIENCE AND ENGINEERING, A271, 395-400 (1999)), solution mixing (solvent evaporation) (C. Stéphan, et al., SYNTHETIC METALS, 108, 139-149 (2000); and K. H. Kim, et al. COMPOSITES SCIENCE AND TECHNOLOGY 68, 2120-2124 (2008)), and mold injection (W. J. Lee, et al. COMPOSITE STRUCTURES, 76, 406-410 (2006)) have been proposed. While these methods show some improvement in the mechanical properties of the composite material, the reinforcement effect of the CNTs is relatively small. Furthermore, the composite materials produced by these methods generally are not transparent. In some instances, the composite materials produced by these methods is black.
At least in certain instances, these properties are due to the difficulties associated with one or more of the following: uniformly dispersing a high concentration of CNTs in matrix materials (especially when long CNTs are used), aligning CNTs in a composite, and the weak interactions between CNTs and a matrix material. Furthermore, the dispersion methods described in the prior art typically cause the resulting composite materials to lose transparency when transparent materials are used as the matrix material. This problem occurs—in some instances—even when the content of CNTs is less than 1 wt %.
Methods are needed that allow CNTs to be used as filler in a composite material that reduces or avoids one or more of these difficulties.